1. Field of the Invention
This invention relates to an endless belt-type sensitive member assembly unit or "module", and more particularly to one where an endless belt-type sensitive member is trained in tension about a plurality of supporting rollers mounted between the side frames of the unit.
2. Discussion of the Prior Art
In a high speed electrophotographic reproducing apparatus which has an endless belt-type photosensitive member and in which an instantaneous exposure is effected by means of a flash lamp, it is required to transport the photosensitive member, i.e., the belt, in a flat or tensioned condition at the moment of exposure, so that the image of an original document may be projected onto the photosensitive member -- or "belt" as it will be referred to hereafter -- in a satisfactory manner. To this end, the unit in which the sensitive member or "belt" is mounted is so constructed that part of the belt, i.e., at least the portion thereof to be exposed to the light image, is usually maintained flat. In addition, because the exposure is instantaneously effected by means of a flash lamp, the belt travels continuously from the exposure station to the developing station, transfer station, etc. without interruption of motion at every exposure.
The belt on the sensitive member assembly unit or "module", as it will be called hereinafter, should travel to the successive stations of the above-mentioned series in a manner that respective corresponding portions of the belt are positioned properly at the related stations, and accordingly there should be provided a special belt-type sensitive member to meet this end in connection with its usage.
Hitherto, a seamless endless belt-type sensitive member has been used, generally being trained in tension about supporting rollers mounted in the module, with at least the portion thereof to be exposed to the light image being maintained in a flat state, as mentioned above. The sensitive member of this type is repeatedly used for reproducing an original document, such that its service life is only about 5,000 to 10,000 reproduction cycles, resulting in the necessity to replace it frequently. Furthermore, for removing a sheet of copying paper stuck in the reproducing apparatus, for removing stains such as toner residues from the belt surface, or for removing dust adhering to the belt surface, the module must be taken out from the main body of the reproducing apparatus where it rests during operation. A sensitive member to be set on the module is of an endless type, hence for facilitating its replacement, all support must be provided within the module, rather than outwardly of its periphery, so as not to interfere with resetting of the endless belt into the unit. As shown in FIG. 1, the construction of a known unit is, for example, such that guide rails C along which a module A is withdrawn from the main body of a reproducing apparatus, are provided within module A, while rails B provided within the reproducing apparatus extend into the interior of A in engaging relation to the aforesaid guide rails C. The rails B are therefore necessarily of a cantilever type supported at only one point D by the reproducing apparatus. For proper support of the heavy module A by the cantilevered rails B, an extremely strong reinforcing member must be provided at the point D where the load is concentrated. Because rails B are supported only at one end, i.e., at point D, the rails B and C become deflected due to the weight of module A during the repeated cycles of withdrawal and reinsertion of module A from and into, respectively, the reproducing apparatus. This deflection results in inaccurate positioning of the exposure, developing, transfer and cleaning stations relative to the belt or sensitive member trained in tension around module A. Inaccurate positioning adversely affects the reproducing function of the apparatus itself, resulting in a poor quality image, such as a defocused or an unevenly developed image.